U.S. patent number 6,490,474 [Application Number 08/905,090] was granted by the patent office on 2002-12-03 for system and method for electrode localization using ultrasound.
This patent grant is currently assigned to Cardiac Pathways Corporation. Invention is credited to Axel Brisken, Marsha Hurd, N. Parker Willis, Jinglin Zeng.
United States Patent |
6,490,474 |
Willis , et al. |
December 3, 2002 |
System and method for electrode localization using ultrasound
Abstract
The present invention is a device localization system that uses
one or more ultrasound reference catheters to establish a fixed
three-dimensional coordinate system within a patient's heart using
principles of triangulation. The coordinate system is represented
graphically in three-dimensions on a video monitor and aids the
clinician in guiding other medical devices, which are provided with
ultrasound transducers, through the body to locations at which they
are needed to perform clinical procedures. In one embodiment of a
system according to the present invention, the system is used in
the heart to help the physician guide mapping catheters for
measuring electrical activity, and ablation catheters for ablating
selected regions of cardiac tissue, to desired locations within the
heart.
Inventors: |
Willis; N. Parker (Atherton,
CA), Brisken; Axel (Fremont, CA), Zeng; Jinglin (San
Jose, CA), Hurd; Marsha (Clayton, CA) |
Assignee: |
Cardiac Pathways Corporation
(Sunnyvale, CA)
|
Family
ID: |
25420280 |
Appl.
No.: |
08/905,090 |
Filed: |
August 1, 1997 |
Current U.S.
Class: |
600/424; 600/374;
606/41; 607/122 |
Current CPC
Class: |
A61B
5/6858 (20130101); A61B 5/287 (20210101); A61B
8/0833 (20130101); A61B 8/445 (20130101); A61B
18/1492 (20130101); A61B 5/6855 (20130101); A61B
5/6856 (20130101); A61B 5/06 (20130101); A61B
8/12 (20130101); A61B 2562/0215 (20170801); A61B
2018/00214 (20130101); A61B 2218/002 (20130101); A61B
2018/00065 (20130101); A61B 2018/00113 (20130101); A61N
2007/0078 (20130101); A61B 2017/00106 (20130101); A61B
2034/2051 (20160201); A61B 2034/2063 (20160201); A61B
2562/043 (20130101); A61B 2018/00577 (20130101); A61B
8/543 (20130101); A61B 2018/00351 (20130101); A61B
2018/00839 (20130101) |
Current International
Class: |
A61B
5/042 (20060101); A61B 8/12 (20060101); A61B
8/08 (20060101); A61B 18/14 (20060101); A61B
5/0408 (20060101); A61B 5/06 (20060101); A61B
005/04 () |
Field of
Search: |
;600/424,374,373,509
;607/122,126 ;606/41,45,49,32,34 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 499 491 |
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Aug 1992 |
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EP |
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775 466 |
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May 1997 |
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EP |
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|
Primary Examiner: Smith; Ruth S.
Attorney, Agent or Firm: Bingham McCutchen LLP
Claims
We claim:
1. A system for tracking the three-dimensional position of a
medical device within a living body, comprising: a reference
catheter having a plurality of ultrasound reference transducers
mounted thereon, the reference catheter positionable within the
living body; an ultrasound target transducer mounted to a medical
device which is to be tracked; localization hardware electronically
coupled to the ultrasound target and reference transducers for
causing a plurality of the ultrasound transducers to transmit
ultrasound signals, for causing a plurality of the ultrasound
transducers to receive ultrasound signals including for causing
ultrasound reference transducers to receive ultrasound signals
emitted by other ultrasound reference transducers, and for
measuring elapsed time between transmission of ultrasound signals
by transmitting transducers and receipt of the signals by receiving
transducers; a graphical display; and processor means
electronically coupled to the localization hardware for calculating
distances between the transducers using the measured elapsed time,
for determining a three-dimensional arrangement of the transducers,
and for generating an image for display on the graphical display
representing a three-dimensional position of at least a portion of
the medical device.
2. The system of claim 1 wherein the system is for tracking the
three-dimensional position of a medical device having a distal tip
and wherein the processor means is for generating an image for
display on the graphical display representing the three-dimensional
position of the distal tip.
3. The system of claim 1 wherein the processor means is for
determining the three-dimensional arrangement of the transducers by
determining the three-dimensional arrangement of the reference
transducers to establish a coordinate system within the body and by
determining the three-dimensional position of the target transducer
relative to the coordinate system.
4. The system of claim 1 wherein the processor means is further for
generating an image for display on the graphical display
representing the three-dimensional position of at least a portion
of the reference catheter.
5. The system of claim 1 wherein the medical device is a mapping
catheter having a mapping electrode.
6. The system of claim 5 wherein the mapping catheter includes a
plurality of ultrasound target transducers.
7. The system of claim 5 wherein the mapping catheter includes an
elongate shaft, a plurality of arms extending from the shaft, and a
plurality of target transducers and mapping electrodes on the arms
of the catheter.
8. The system of claim 7 wherein the processor means is further for
deriving the three-dimensional positions of the arms and for
generating an image for display on the graphical display
representing the three-dimensional position of at least a portion
of each arm.
9. The system of claim 7 wherein the mapping catheter comprises
both the reference catheter and the medical device.
10. The method of claim 5, wherein the mapping and reference
catheters are separate.
11. The system of claim 1 wherein the reference catheter is a
mapping catheter having at least one electrode.
12. The system of claim 1 wherein the medical device is a catheter
having an electrode and wherein the processor means is further for
deriving the three-dimensional position of the electrode and for
generating an image for display on the graphical display
representing the three-dimensional position of the electrode.
13. The system of claim 1 wherein the reference catheter comprises
a single spline on which the ultrasound reference transducers are
mounted.
14. A system for tracking the three-dimensional position of a
medical device within a living body, comprising: a reference
catheter having a plurality of ultrasound reference transducers
mounted thereon, the reference catheter positionable within the
living body; an ultrasound target transducer mounted to a medical
device which is to be tracked, the medical device having an
electrode; localization hardware electronically coupled to the
ultrasound target and reference transducers for causing a plurality
of the ultrasound transducers to transmit ultrasound signals, for
causing a plurality of the ultrasound transducers to receive
ultrasound signals including for causing ultrasound reference
transducers to receive ultrasound signals emitted by other
ultrasound reference transducers, and for measuring elapsed time
between transmission of ultrasound signals by transmitting
transducers and receipt of the signals by receiving transducers; a
graphical display; and processor means electronically coupled to
the localization hardware for calculating distances between the
transducers using the measured elapsed time, for establishing a
coordinate system using the calculated distances, for determining a
three-dimensional position of the target transducer relative to the
coordinate system, for using the three-dimensional position of the
target transducer to derive a three-dimensional position of the
electrode relative to the coordinate system, and for generating an
image for display on the graphical display representing a
three-dimensional position of the electrode.
15. The system of claim 14 wherein the processor means is further
for using the three-dimensional position of the target transducer
to derive the three-dimensional position and orientation of the
catheter relative to the coordinate system, and for generating an
image for display on the graphical display representing the
three-dimensional position and orientation of at least a portion of
the catheter.
16. The system of claim 14 wherein the reference catheter has an
electrode.
17. The system of claim 14 wherein the reference catheter comprises
a single spline on which the ultrasound reference transducers are
mounted.
18. A system for diagnosing and/or treating cardiac arrhythmias,
the system comprising: a plurality of ultrasound reference
transducers, the reference transducers mounted on at least one
reference catheter positionable within a patient's chest; a mapping
catheter having a mapping portion including at least one mapping
electrode and at least one ultrasound target transducer adjacent to
the mapping catheter; localization hardware electronically coupled
to the target and reference transducers for causing a plurality of
the ultrasound transducers to transmit ultrasound signals, for
causing a plurality of the ultrasound transducers to receive
ultrasound signals including for causing ultrasound reference
transducers to receive ultrasound signals emitted by other
ultrasound reference transducers, and for measuring elapsed time
between transmission of ultrasound signals by transmitting
transducers and receipt of the signals by receiving transducers;
electrophysiology hardware electronically coupled to the mapping
electrode for receiving mapping signals corresponding to electrical
activity measured by the mapping electrodes; a graphical display;
and processor means electronically coupled to the localization
hardware for calculating distances between the transducers using
the measured elapsed time; for determining a three-dimensional
arrangement of the transducers, for receiving mapping signals from
the electrophysiology hardware, and for generating an image for
display on the graphical display representing a three-dimensional
position of at least a portion of the mapping catheter.
19. The system of claim 18 wherein the reference catheter has a
mapping electrode.
20. The system of claim 18 wherein the processor means is for
determining the three-dimensional arrangement of the transducers by
determining the three-dimensional arrangement of the reference
transducers to establish a coordinate system within the body and by
determining the three-dimensional position of the target transducer
relative to the coordinate system.
21. The system of claim 18 wherein the processor means further
generates data representing the received mapping signals for
display on the graphical display.
22. The system of claim 18 wherein the processor means is for
displaying the data representing the received mapping signals on
the graphical display at a location corresponding to the
three-dimensional positions of the mapping electrodes.
23. The system of claim 22 wherein the processor means is for
generating an isochronal map displaying the data representing the
received mapping signals on the graphical display at a location
corresponding to the three-dimensional positions of the mapping
electrodes.
24. The system of claim 22 wherein the processor means is for
generating an isopotential map displaying the data representing the
received mapping signals on the graphical display at a location
corresponding to the three-dimensional positions of the mapping
electrodes.
25. The system of claim 21 wherein the mapping catheter includes:
an elongate shaft; a plurality of arms extending from the shaft; a
plurality of the mapping electrodes carried on the arms; and a
plurality of ultrasound tracking transducers on the arms.
26. The system of claim 18 wherein: the system further comprises an
ablation catheter having an ablation section, an ablation electrode
at the ablation section for forming lesions in the heart, and an
ultrasound tracking transducer; the localization hardware is
electronically coupled to the ultrasound tracking transducer on the
ablation catheter; and the processor means is further for
generating an image which represents the three-dimensional position
of at least a portion of the ablation section of the ablation
catheter.
27. The system of claim 26 wherein the processor means is further
for, with the ablation section at a target location at which a
lesion has been formed, using the measured elapsed time for
calculating the distances between the ultrasound tracking
transducer on the ablation catheter and the other ultrasound
transducers, for determining the three-dimensional location of the
ablation section using the calculated distances, and for generating
an image for selective display on the graphical display which
represents the three-dimensional position of at least a portion of
the lesion.
28. The system of claim 18 wherein: the system further comprises a
marking catheter having a distal tip and an ultrasound transducer;
the localization hardware is electronically coupled to the
ultrasound transducer on the marking catheter; the processor means
is further for deriving the three-dimensional position of the
distal tip from the three-dimensional position of the ultrasound
transducer on the marking catheter.
29. The system of claim 28 wherein the processor means is further
for generating an image which includes the derived
three-dimensional position of the distal tip.
30. The system of claim 18 wherein the reference catheter comprises
a single spline on which the ultrasound reference transducers are
mounted.
31. The method of claim 18, wherein the mapping and reference
catheters are separate.
32. An electrode localization and ablation system, comprising: a
reference catheter having a plurality of ultrasound reference
transducers mounted thereon, the reference catheter positionable
within the living body; an ablation catheter having an ablation
section including at least one ablation electrode for forming
lesions and at least one ultrasound target transducer; localization
hardware electronically coupled to the target and reference
transducers for causing a plurality of the ultrasound transducers
to transmit ultrasound signals, for causing a plurality of the
ultrasound transducers to receive ultrasound signals including for
causing ultrasound reference transducers to receive ultrasound
signals emitted by other ultrasound reference transducers, and for
measuring elapsed time between transmission of ultrasound signals
by transmitting transducers and receipt of the signals by receiving
transducers; a source of ablation energy electrically coupled to
the ablation electrode to cause the ablation electrode to generate
lesions within the living body; a graphical display; and processor
means electronically coupled to the localization hardware for
calculating distances between the transducers using the measured
elapsed time, for determining a three-dimensional arrangement of
the transducers, and for generating an image for display on the
graphical display representing a three-dimensional position of at
least a portion of the ablation section.
33. The system of claim 32 wherein the processor means is further
for, with the ablation section at a target location at which a
lesion has been formed, using the measured elapsed time for
calculating the distances between the ultrasound tracking
transducer on the ablation catheter and the other ultrasound
transducers, for determining the three-dimensional location of the
ablation section using the calculated distances, and for generating
an image for selective display on the graphical display which
represents the three-dimensional position of at least a portion of
the lesion.
34. The system of claim 32 wherein the processor means is for
determining the three-dimensional arrangement of the transducers by
determining the three-dimensional arrangement of the referenc e
transducers to establish a coordinate system within the body and by
determining the three-dimensional position of the target transducer
relative to the coordinate system.
35. The system of claim 32 wherein the reference catheter comprises
a single spline on which the ultrasound reference transducers are
mounted.
36. A method of tracking the position of a target catheter within a
chamber of a living heart, comprising the steps of: positioning a
reference catheter inside the body, near the heart, with the
reference catheter having a plurality of ultrasound transducers
mounted thereon; positioning a target catheter within a chamber of
the heart, the target catheter having at least one ultrasound
transducer mounted thereon; causing a plurality of the transducers
to generate ultrasound signals, causing a plurality of the
transducers to receive ultrasound signals, including causing
ultrasound reference transducers to receive ultrasound signals
emitted by other ultrasound reference transducers, and recording
elapsed time between the generation of signals from each
transmitting one of the transducers and the receipt of signals by
receiving ones of the transducers; determining a location of the
target catheter with respect to the reference catheter based on the
recorded times; and displaying a location of at least a portion of
the target catheter on a graphical display.
37. The method of claim 36, further comprising the step of using
one of the catheters to measure the electrical activity of the
heart.
38. The method of claim 36, further comprising the step of using
one of the catheters to ablate cardiac tissue.
39. The method of claim 36 wherein the reference catheter is
positioned in the heart and/or coronary vasculature.
40. The method of claim 36 wherein the location of the target
catheter is determined using a triangulation algorithm.
41. The method of claim 36 wherein the reference catheter comprises
a single spline on which the ultrasound reference transducers are
mounted.
42. The method of claim 36 wherein the reference catheter is
positioned within the coronary sinus of the heart.
43. A method of tracking the position of a medical device within a
living body, comprising the steps of: (a) providing a reference
catheter having a plurality of ultrasound reference transducers,
each reference transducer capable of transmitting and receiving
ultrasound signals; (b) providing a medical device, the medical
device including an ultrasound target transducer; (c) positioning
the reference catheter and the medical device within the living
body; (d) causing a plurality of the transducers to transmit
ultrasound signals for receipt by others of the transducers,
including causing ultrasound reference transducers to receive
ultrasound signals emitted by other ultrasound reference
transducers; (e) measuring elapsed time between transmission of
each ultrasound signal emitted in step (d) and its receipt by each
of the other transducers, and using the measured elapsed time to
determine relative distances between the transducers; (f) using
distances determined in step (e), establishing a three-dimensional
arrangement of the reference transducers to establish a coordinate
system within the body, and determining a location of the medical
device relative to the coordinate system; and (g) displaying a
three-dimensional position of at least a portion of the target
transducer relative to the coordinate system on a graphical
display.
44. The method of claim 43 wherein the medical device provided in
step (b) is a mapping catheter having a mapping electrode, and
wherein the method further comprises the steps of: (h) positioning
the mapping electrode at a location within the living body; (i)
measuring electrical activity from the electrode; and (j) deriving
the three-dimensional position of the electrode from the
three-dimensional position of the target transducer and graphically
representing mapping signals corresponding to electrical activity
measured by the electrode on the graphical display at the three
dimensional position of the electrode.
45. The method of claim 44 wherein the mapping catheter provided in
step (b) includes multiple mapping electrodes and a plurality of
target transducers, and wherein: step (h) includes simultaneously
positioning a plurality of the mapping electrodes at a location;
step (i) includes measuring the electrical activity with the
plurality of electrodes; and step (j) includes deriving the
three-dimensional positions of the electrodes using the
three-dimensional positions of the target transducers and
simultaneously displaying electrical activity measured by each of a
plurality of the mapping electrodes on the graphical display at the
three dimensional position of its corresponding electrode.
46. The method of claim 45 wherein the mapping catheter provided in
step (b) includes an elongate shaft, a plurality of arms extending
from the shaft, a plurality of mapping electrodes on the arms, and
a plurality of ultrasound transducers on the arms, and wherein the
reference catheter provided in step (a) comprises the mapping
catheter.
47. The method of claim 44 wherein the mapping catheter provided in
step (b) includes multiple mapping electrodes and a plurality of
target transducers, and wherein: step (h) includes simultaneously
positioning a plurality of the mapping electrodes at a location;
step (i) includes measuring the electrical activity with the
plurality of electrodes; and step (j) includes deriving the
three-dimensional positions of the electrodes using the
three-dimensional positions of the target transducers and
graphically displaying parameters derived from the measured
electrical activity on the graphical display at the three
dimensional position of at least a portion of the electrodes.
48. The method of claim 44, wherein the mapping and reference
catheters are separate.
49. The method of claim 43 wherein the medical device provided in
step (b) is a mapping catheter having a mapping electrode, and
wherein the method further comprises the steps of: (h) positioning
the mapping electrode at a location within the living body; (i)
measuring electrical activity from the electrode; and (j) deriving
the three-dimensional position of the electrode from the
three-dimensional position of the target transducer and graphically
representing parameters derived from the measured electrical
activity on the graphical display at the three dimensional position
of the electrode.
50. The method of claim 49 wherein: step (b) further provides a
second medical device in the form of an ablation catheter having an
ablation section including an ablation electrode and a target
transducer, and wherein the method further includes: (k) evaluating
the display created at step (j) to identify a target location for
ablation; (l) moving the ablation catheter towards the target
location in the body while tracking the location of the ablation
catheter relative to the coordinate system; (m) graphically
representing the location of the ablation section on the graphical
display; (o) while observing the graphical display, repeating steps
(l) and (m) until the graphical display shows the ablation section
at the target location; and (p) supplying ablation energy to the
ablation electrode to induce ablation at the target location.
51. The method of claim 49, wherein the mapping and reference
catheters are separate.
52. The method of claim 43 wherein the method is for tracking the
position of a catheter within a patient's heart, and wherein: step
(a) provides a reference catheter having a distal tip; step (c)
includes positioning the reference catheter in the right ventricle
of the patient's heart with the distal tip at the right ventricular
apex.
53. The method of claim 52 wherein; step (a) provides a second
reference catheter; step (c) includes positioning the second
reference catheter in the coronary sinus of the patient's
heart.
54. The method of claim 43, wherein the method is for tracking the
position of a catheter within a patient's heart, wherein the
patient's heart has a cardiac cycle, and wherein the method further
comprises the step of storing data representing the
three-dimensional position of at least a portion of the catheter at
a selected portion of the cardiac cycle.
55. The method of claim 43 wherein the method is for tracking the
position of a catheter within a patient's heart, and wherein: step
(a) provides a reference catheter; step (c) includes positioning
the reference catheter in the coronary sinus of the patient's
heart.
56. The method of claim 43, further including the step of using the
relative distances established in step (e), deriving the
three-dimensional position and orientation of the reference
catheter and displaying an image representing the three-dimensional
position and orientation of at least a portion of the reference
catheter on the graphical display.
57. The method of claim 43, further including the step of repeating
steps (d) through (g) while moving the medical device to a location
within the living body.
58. The method of claim 43 wherein step (e) includes using a
triangulation algorithm to determine the location of the target
transducer.
59. The method of claim 43 wherein the medical device provided in
step (b) is an ablation device having an ablation electrode, and
wherein the method further comprises the steps of: (h) positioning
the ablation electrode at a target location within the living body;
(i) delivering ablation energy to the electrode to induce ablation
at the target location and to thereby form a lesion; and (j)
extrapolating the three-dimensional position of at least a portion
of the lesion from the three-dimensional location of the target
transducer established in step (f); and (k) including the
three-dimensional location of the lesion determined in step (j) on
the graphical display.
60. The method of claim 43 wherein the medical device is a marking
catheter having a distal portion and wherein the ultrasound
tracking transducer is located at the distal portion, and wherein:
step (c) includes manipulating the marking catheter under
fluoroscopic visualization to position the target transducer
adjacent to a predetermined anatomical structure within the body;
and the method further includes the step of extrapolating the
position of the anatomical structure from the three-dimensional
position of the target transducer determined in step (f) and
displaying the three-dimensional position of the anatomical
structure on the graphical display.
61. The method of claim 43 wherein the reference catheter comprises
a single spline on which the ultrasound reference transducers are
mounted.
62. The method of claim 43, wherein the reference catheter is
positioned within the coronary sinus of the heart.
63. A system for tracking the three-dimensional position of a
medical device within a living body, comprising: a plurality of
reference catheters, each reference catheter having at least one
ultrasound reference transducer mounted thereon and being
positionable within the living body; an ultrasound target
transducer mounted to a medical device which is to be tracked;
localization hardware electronically coupled to the ultrasound
target and reference transducers for causing a plurality of the
ultrasound transducers to transmit ultrasound signals, for causing
a plurality of the ultrasound transducers to receive ultrasound
signals including for causing ultrasound reference transducers to
receive ultrasound signals emitted by other ultrasound reference
transducers, and for measuring elapsed time between transmission of
ultrasound signals by transmitting transducers and receipt of the
signals by receiving transducers; a graphical display; and
processor means electronically coupled to the localization hardware
for calculating distances between the transducers using the
measured elapsed time, for determining a three-dimensional
arrangement of the transducers, and for generating an image for
display on the graphical display representing a three-dimensional
position of at least a portion of the medical device.
64. The system of claim 63 wherein at least one of the reference
catheters has at least two ultrasound reference transducers
thereon.
65. A system for tracking the three-dimensional position of a
medical device within a living body, comprising: a plurality of
reference catheters, each having at least one ultrasound transducer
mounted thereon, the reference catheters positionable within a
living body; an ultrasound target transducer mounted to a medical
device which is to be tracked, the medical device having an
electrode; localization hardware electronically coupled to the
ultrasound target and reference transducers for causing a plurality
of the ultrasound transducers to transmit ultrasound signals, for
causing a plurality of the ultrasound transducers to receive
ultrasound signals including for causing ultrasound reference
transducers to receive ultrasound signals emitted by other
ultrasound reference transducers, and for measuring elapsed time
between transmission of ultrasound signals by transmitting
transducers and receipt of the signals by receiving transducers; a
graphical display; and processor means electronically coupled to
the localization hardware for calculating distances between the
transducers using the measured elapsed time, for establishing a
coordinate system using the calculated distances, for determining a
three-dimensional position of the target transducer relative to the
coordinate system, for using the three-dimensional position of the
target transducer to derive a three-dimensional position of the
electrode relative to the coordinate system, and for generating an
image for display on the graphical display representing a
three-dimensional position of the electrode.
66. The system of claim 65 wherein at least one of the reference
catheters has at least two ultrasound transducers thereon.
67. The system of claim 65 wherein each of the reference catheters
comprises a single spline on which the ultrasound reference
transducers are mounted.
68. A system for diagnosing and/or treating cardiac arrhythmias,
the system comprising: a plurality of reference catheters, each
having at least one ultrasound reference transducer mounted
thereon, the reference catheters positionable within a patient's
chest; a mapping catheter having a mapping portion including at
least one mapping electrode and at least one ultrasound target
transducer adjacent to the mapping catheter; localization hardware
electronically coupled to the target and reference transducers for
causing a plurality of the ultrasound transducers to transmit
ultrasound signals, for causing a plurality of the ultrasound
transducers to receive ultrasound signals including for causing
ultrasound reference transducers to receive ultrasound signals
emitted by other ultrasound reference transducers, and for
measuring elapsed time between transmission of ultrasound signals
by transmitting transducers and receipt of the signals by receiving
transducers; electrophysiology hardware electronically coupled to
the mapping electrode for receiving mapping signals corresponding
to electrical activity measured by the mapping electrodes; a
graphical display; and processor means electronically coupled to
the localization hardware for calculating distances between the
transducers using the measured elapsed time, for determining a
three-dimensional arrangement of the transducers, for receiving
mapping signals from the electrophysiology hardware, and for
generating an image for display on the graphical display
representing a three-dimensional position of at least a portion of
the mapping catheter.
69. The system of claim 68, wherein at least one of the reference
transducers has at least two ultrasound reference transducers
thereon.
70. The system of claim 68 wherein each of the reference catheters
comprises a single spline on which the ultrasound reference
transducers are mounted.
71. An electrode localization and ablation system, comprising: a
plurality of reference catheters, each having at least one
ultrasound reference transducer mounted thereon, the reference
catheters positionable within a living body; an ablation catheter
having an ablation section including at least one ablation
electrode for forming lesions and at least one ultrasound target
transducer; localization hardware electronically coupled to the
target and reference transducers for causing a plurality of the
ultrasound transducers to transmit ultrasound signals, for causing
a plurality of the ultrasound transducers to receive ultrasound
signals including for causing ultrasound reference transducers to
receive ultrasound signals emitted by other ultrasound reference
transducers, and for measuring elapsed time between transmission of
ultrasound signals by transmitting transducers and receipt of the
signals by receiving transducers; a source of ablation energy
electrically coupled to the ablation electrode to cause the
ablation electrode to generate lesions within the living body; a
graphical display; and processor means electronically coupled to
the localization hardware for calculating distances between the
transducers using the measured elapsed time, for determining a
three-dimensional arrangement of the transducers, and for
generating an image for display on the graphical display
representing a three-dimensional position of at least a portion of
the ablation section.
72. The system of claim 71 wherein at least one of the reference
catheters has at least two ultrasound reference transducers
thereon.
73. The system of claim 71 wherein each of the reference catheters
comprises a single spline on which the ultrasound reference
transducers are mounted.
74. A method of tracking the position of a target catheter within a
chamber of a living heart, comprising the steps of: positioning a
plurality of reference catheters inside the body, near the heart,
with each reference catheter having at least one ultrasound mounted
thereon; positioning a target catheter within a chamber of the
heart, the target catheter having at least one ultrasound
transducer mounted thereon; causing a plurality of the transducers
to generate ultrasound signals, causing a plurality of the
transducers to receive ultrasound signals, including causing
ultrasound reference transducers to receive ultrasound signals
emitted by other ultrasound reference transducers, and recording
elapsed time between the generation of signals from each
transmitting one of the transducers and the receipt of signals by
receiving ones of the transducers; determining a location of the
target catheter with respect to the reference catheter based on the
recorded times; and displaying a location of at least a portion of
the target catheter on a graphical display.
75. The method of claim 74 where at least one of the reference
catheters has at least two ultrasound reference transducers
thereon.
76. The method of claim 74 wherein each of the reference catheters
comprises a single spline on which the ultrasound reference
transducers are mounted.
77. The method of claim 74, wherein one of the reference catheters
is positioned within the coronary sinus of the heart.
78. The method of claim 74, wherein one of the reference catheters
is positioned within the coronary sinus of the heart, and another
of the reference catheters is positioned in the right ventricle of
the heart.
79. A method of tracking the position of a medical device within a
living body, comprising the steps of: (a) providing a plurality of
reference catheters, each reference catheter including at least one
reference transducer capable of transmitting and receiving
ultrasound signals; (b) providing a medical device, the medical
device including an ultrasound target transducer; (c) positioning
the reference catheter and the medical device within the living
body; (d) causing a plurality of the transducers to transmit
ultrasound signals for receipt by others of the transducers,
including causing ultrasound reference transducers to receive
ultrasound signals emitted by other ultrasound reference
transducers; (e) measuring elapsed time between transmission of
each ultrasound signal emitted in step (d) and its receipt by each
of the other transducers, and using the measured elapsed time to
determine relative distances between the transducers; (f) using
distances determined in step (e), establishing a three-dimensional
arrangement of the reference transducers to establish a coordinate
system within the body, and determining a location of the medical
device relative to the coordinate system; and (g) displaying a
three-dimensional position of at least a portion of the target
transducer relative to the coordinate system on a graphical
display.
80. The method of claim 79 wherein at least one of the reference
catheters has at least two ultrasound reference transducers capable
of transmitting and receiving ultrasound signals.
81. The method of claim 79 wherein each of the reference catheters
comprises a single spline on which the ultrasound reference
transducers are mounted.
82. The method of claim 79, wherein one of the reference catheters
is positioned within the coronary sinus of the heart.
83. The method of claim 79, wherein one of the reference catheters
is positioned within the coronary sinus of the heart, and another
of the reference catheters is positioned in the right ventricle of
the heart.
Description
FIELD OF THE INVENTION
The present invention relates generally to the field of ultrasound
tracking systems. More specifically, it relates to systems for
tracking the positions of devices within the human body.
BACKGROUND OF THE INVENTION
For certain types of minimally invasive medical procedures,
endoscopic visualization of the treatment site within the body is
unavailable or does not assist the clinician in guiding the needed
medical devices to the treatment site.
Examples of such procedures are those used to diagnose and treat
supra-ventricular tachycardia (SVT), atrial fibrillation (AF),
atrial flutter (AFL) and ventricular tachycardia (VT). SVT, AFL, AF
and VT are conditions in the heart which cause abnormal electrical
signals to be generated in the endocardial tissue to cause
irregular beating of the heart.
A procedure for diagnosing and treating SVT or VT involves
measuring the electrical activity of the heart using an
electrophysiology catheter introduced into the heart via the
patient's vasculature. The catheter carries mapping electrodes
which are positioned within the heart and used to measure
electrical activity. The position of the catheter within the heart
is ascertained using fluoroscopic images. A map of the measured
activity is created based on the fluoroscopic images and is shown
on a graphical display. A physician uses the map to identify the
region of the endocardium which s/he believes to be the source of
the abnormal electrical activity. An ablation catheter is then
inserted through the patient's vasculature and into the heart where
it is used to ablate the region identified by the physician.
To treat atrial fibrillation (AF), an ablation catheter is
maneuvered into the right or left atrium where it is used to create
elongated ablation lesions in the heart. These lesions are intended
to stop the irregular beating of the heart by creating
non-conductive barriers between regions of the atria. These
barriers halt passage through the heart of the abnormal electrical
activity generated by the endocardium. Following the ablation
procedure, a mapping catheter is positioned in the heart where it
is used to measure the electrical activity within the atria so that
the physician may evaluate whether additional lesions are needed to
form a sufficient line of block against passage of abnormal
currents. S/he may also attempt to induce atrial fibrillation using
a pacing electrode, and then further evaluate the line of block by
analyzing the time required for the induced electrical activity to
pass from one side of the block to the other.
The procedures used to diagnose and treat SVT, VT, AFL and AF
utilize catheters which are maneuvered within the heart under
fluoroscopy. Because the fluoroscopic image is in two-dimensions
and has fairly poor resolution, it may be difficult for the
physician to be certain of the catheter positions. Thus, for
example, once a physician has identified an area which is to be
ablated (using a map of the measured electrical activity of the
heart) it may be difficult to navigate an ablation catheter to the
appropriate location in order to accurately ablate the area of
concern. It is therefore desirable to provide a system by which the
positions of medical devices such as mapping and ablation catheters
may be accurately guided to selected regions of the body.
Prior art tracking devices of the type which may track the
positions of medical devices are described in U.S. Pat. No.
5,515,853 (Smith et al) and U.S. Pat. No. 5,546,951 (Ben Haim).
While useful, neither of the disclosed systems provides for
determining medical device locations relative to a fixed coordinate
system within the body. The lack of a fixed coordinate system
within the body can lead to tracking errors which in turn render it
difficult to guide medical devices to the desired locations within
the body.
It is therefore desirable to provide an ultrasound tracking system
for medical devices which permits the tracking of devices relative
to a fixed internal coordinate system. The system according to the
present invention meets this objective as well as many others which
enhance the accuracy and usefulness of the tracking system.
SUMMARY OF THE INVENTION
The present invention is a device localization system that uses one
or more ultrasound reference catheters to establish a fixed
three-dimensional coordinate system within a patient's heart,
preferably using principles of triangulation. The coordinate system
is represented graphically in three-dimensions on a video monitor
and aids the clinician in guiding other medical devices, which also
carry ultrasound transducers, through the body to locations at
which they are needed to perform clinical procedures. In one
embodiment of a system according to the present invention, the
system is used in the heart to help the physician guide mapping
catheters for measuring electrical activity, and ablation catheters
for ablating selected regions of cardiac tissue, to desired
locations within the heart.
Three-dimensional images are shown on a video display which
represent the three-dimensional positions and orientations of at
least portions of the medical devices used with the system, such as
the reference catheter, and the electrodes of the mapping catheter
and ablation catheter. The video display may additionally include
representations of the electrical activity measured by each mapping
electrode at its respective location on the three-dimensional
display. It may also represent ablation lesions formed within the
body at the appropriate three-dimensional locations, and/or certain
anatomic structures which may facilitate navigation of the medical
device(s) within the patient.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of the system according to the
present invention, showing the major components of the system.
FIG. 2 is a schematic representation of a three-dimensional
coordinate system established using a reference catheter according
to the present invention.
FIG. 3 is a side elevation view of a reference catheter for use
with the system according to the present invention.
FIG. 4 is a side elevation view of a first alternative embodiment
of a reference catheter for use with the system according to the
present invention, in which ultrasound transducers are included on
a catheter of a type conventionally used in the RV apex.
FIG. 5 is a side elevation view of a second alternative embodiment
of a reference catheter for use with the system according to the
present invention, in which ultrasound transducers are included on
a catheter of a type conventionally used in the coronary sinus.
FIG. 6 is a perspective view of a piezoelectric cylinder of a type
which may be used on catheters according to the present invention,
including those shown in FIGS. 3-5.
FIG. 7 is a side elevation view of the piezoelectric cylinder of
FIG. 6 mounted on a catheter and modified to include a divergent
lens.
FIG. 8 is a perspective view of a mandrel having a polymer
piezoelectric wrapped around it for use with a reference catheter
according to the present invention.
FIG. 9 is a side elevation view of a catheter for use with the
system of the present invention which is provided with marking and
ablation capabilities.
FIG. 10 is a perspective view of a first alternative embodiment of
a catheter with marking and ablation capabilities according to the
present invention.
FIGS. 11 and 12 are side section views of second and third
alternative embodiments of catheters having marking and ablation
capabilities according to the present invention.
FIG. 13 is a side elevation view of a mapping catheter for use with
the system of the present invention. As with all of the catheters
shown herein, the sizes of the electrodes and transducers are
exaggerated for purposes of illustration.
FIG. 14A is a front elevation view of the mapping catheter of FIG.
13, showing the spacing of the basket arms.
FIG. 14B is a view similar to the view of FIG. 14A showing
alternate basket arm spacing.
FIG. 15 is a cross-section view of the mapping catheter taken along
the plane designated 15--15 in FIG. 13.
FIG. 16 is a plan view of an arm of the mapping catheter of FIG.
13.
FIG. 17 is a cross-section view of the arm of FIG. 16, taken along
the plane designated 17--17.
FIG. 18 is a side elevation view of a linear lesion catheter for
use in the system according to the present invention.
FIG. 19 is a side section view of the linear lesion catheter of
FIG. 18.
FIG. 20 is a cross-section view taken along the plane designated
20--20 in FIG. 19.
FIG. 21 is a cross-section view taken along the plane designated
21--21 in FIG. 19.
FIG. 22 is a cross-section view taken along the plane designated.
22--22 in FIG. 19.
FIG. 23 is a side section view, similar to the view of FIG. 19, of
an alternative embodiment of a linear lesion catheter for use with
the system of the present invention.
FIG. 24 is a cross-section view taken along the plane designated
24--24 in FIG. 23.
FIG. 25 is a side section view, similar to the view of FIG. 19, of
an alternative embodiment of a linear lesion catheter for use with
the system of the present invention.
FIG. 26 is a cross-section view taken along the plane designated
26--26 in FIG. 25.
FIG. 27A is a schematic drawing showing ultrasound ranging hardware
and its interaction with the ultrasound hardware control and timing
systems.
FIG. 27B is a schematic diagram illustrating in greater detail
ultrasound ranging hardware and ultrasound hardware control and
timing systems of the type shown in FIG. 27A.
FIG. 28A is a plot of the voltage over time on an ultrasound
transmit line following initiation of a transmit pulse, and
illustrates the ringing which occurs on the transmit line following
the transmit pulse.
FIG. 28B is a plot of the voltage over time on an ultrasound
receive line which is located near the transmit line at the time
the transmit pulse of FIG. 28A is initiated. The figure shows the
ringing which results from the ringing on the transmit line, and
also shows a receive pulse following the ringing.
FIG. 28C is a plot of the voltage over time on an ultrasound
receive line which is located very close to a transmit wire at the
time the transmit pulse of FIG. 28A is instituted, and it
illustrates that the receive pulse may be lost in the ringing.
FIG. 28D is a plot of the voltage over time on an ultrasound
transmit line which is short circuited immediately following the
initiation of a transmit pulse.
FIG. 28E is a plot of the voltage over time on an ultrasound
receive line which is adjacent to the transmit line represented in
FIG. 28D. The figure shows that ringing is eliminated on the
receive line when the transmit line is short circuited just after
the transmit pulse is sent.
FIG. 29 is a schematic diagram illustrating a pulse generator
circuit which includes a switch for short circuiting the transmit
line just after the transmit pulse is sent.
FIG. 30A is a schematic illustration of the sample and hold system
used for gating position information to the cardiac cycle.
FIG. 30B shows an EKG plot together with a plot of transducer
coordinates and illustrates a sample and hold sequence which takes
transducer coordinates at the end of diastole.
FIGS. 31 and 32 illustrate the graphical user interface of the
system according to the present invention. FIG. 31 illustrates
display of anatomical features, reference catheters, a linear
lesion catheter, and burns formed in the heart using the linear
lesion catheter. FIG. 32 illustrates display of the reference
catheters, anatomical features, burns formed in the heart, and a
basket catheter together with its mapping electrode positions.
FIG. 33 is a flow diagram illustrating use of the catheters of
FIGS. 3, 9 and 13 to treat ventricular tachycardia.
FIGS. 34A-34C are a series of views of a heart illustrating certain
of the steps of FIG. 33: FIG. 34A is an anterior section view of
the heart showing placement of a reference catheter in the right
ventricle and a marking catheter in the left ventricle. FIG. 34B is
a lateral view of the heart showing a reference catheter in the
coronary sinus. FIG. 34C is an anterior section view of the heart
showing a reference catheter in the right ventricle and a mapping
catheter in the left ventricle.
FIG. 34D is a view similar to the view of FIG. 34C showing
introduction of an ablation catheter into the mapping catheter.
FIG. 35 is a flow diagram illustrating use of the system according
to the present invention together with the catheters of FIGS. 3, 9,
13 and 18 to treat atrial fibrillation.
FIGS. 36A-36C are a series of views of a heart illustrating certain
of the steps of FIG. 35: FIG. 36A is an anterior section view of
the heart showing placement of a reference catheter in the RV apex
and a marking catheter in left atria; FIG. 36B is an anterior
section view of the heart showing a linear lesion ablation catheter
in the left atria; FIG. 36C is an anterior section view of the
heart showing a mapping catheter in the left atria.
DETAILED DESCRIPTION
Localization System Overview
The localization system and procedure will next be described in
general terms. Specific examples of procedures which may be carried
out using the system will be described in the Operation section of
this description. The system is described primarily with respect to
catheters in the heart, but it should be understood that the system
is intended for use with other medical devices and in other regions
of the body as well.
Referring to FIG. 1, the present invention is a device localization
system 100 that uses one or more ultrasound reference catheters 10
to establish a three-dimensional coordinate system within a
patient's heart. The system allows the positions of one or more
additional catheters 12, 14, 16, to be represented graphically on a
graphical user interface 124 relative to a coordinate system. This
aids the clinician in guiding the additional catheters 12, 14, 16
through the heart to locations at which they are needed to perform
clinical procedures.
In one embodiment of a system according to the present invention,
the additional catheters include mapping catheters 14 for measuring
electrical activity within the heart and ablation catheters 12, 16
for ablating selected regions of cardiac tissue. These catheters
12-16 may also be described as "electrophysiology catheters" or "EP
catheters."
Each of the reference catheters 10 carries a plurality of
ultrasound transducers, with there being a total of at least four
such transducers employed during use of the system. The reference
catheter transducers can function as ultrasound receivers by
converting acoustic pressure to voltage, and as ultrasound
transmitters by converting voltage to acoustic pressure. Each of
the additional catheters 12, 14, 16 carries at least one ultrasound
transducer which preferably functions as an ultrasound receiver but
which may also function as a transmitter or a
transmitter/receiver.
Using known techniques, the distance between each transducer and
other ones of the transducers may be computed by measuring the
respective time for an ultrasound pulse to travel from a
transmitting transducer to each receiving transducer. These
distance measurements are preferably carried out in parallel. In
other words, when an ultrasound pulse is emitted by a reference
catheter transducer, the system simultaneously measures the
respective times it takes for the pulse to reach each of the other
transducers being used in the system.
The velocity of an acoustic signal in the heart is approximately
1570-1580 mm/msec, with very small variations caused by blood and
tissue. The time for an acoustic pulse to travel from one
transducer to another may therefore be converted to the distance
between the transducers by multiplying the time of flight by the
velocity of an acoustic pulse in the heart (i.e. by 1570-1580
mm/msec). As detailed below, the system of the present invention
uses this "time of flight" principal in combination with the
geometric principal of triangulation to establish a
three-dimensional coordinate system using the reference transducers
on the reference catheter 10, and to then use the additional
catheter transducers to track the location of an additional
catheter 12, 14, 16, relative to the coordinate system.
During use of the system of the invention, one or more of the
reference catheters 10 is introduced into the heart or the
surrounding vasculature (or even into other areas such as the
esophagus) and is left in place for the duration of the procedure.
Once reference catheter(s) 10 are positioned within or near a
patient's heart, the system first measures the distances between
each of the reference catheter transducers using the "time of
flight" principal. It then uses these distances to establish the
relative positions of the reference transducers and therefore to
establish a three-dimensional coordinate system.
Referring to FIG. 2, establishing the coordinate system requires
placement of the reference catheter(s) 10 such that at least four
reference transducers, designated T.sub.REF1 through T.sub.REF4 in
FIG. 2, are available to define a 3-dimensional coordinate system
as follows: T.sub.REF1 through T.sub.REF3, define the plane P at
z=0; one reference transducer T.sub.REF1 defines the origin of the
coordinate system; a line between T.sub.REF3 and T.sub.REF2 defines
the x-axis of the system; and T.sub.REF3 lies in the plane z=0. The
fourth reference transducer, T.sub.REF4, lies on one side of the
plane P, at z>0. Given these constraints, the coordinates of the
reference transducers can be computed using the law of cosines.
See, for example, Advanced Mathematics, A preparation for calculus,
2nd Ed., Coxford, A. F., Payne J. N., Harcort Brace Jovanovich, New
York, 1978, p. 160.
Each of the reference transducers T.sub.REF1 through T.sub.REF4
must be capable of both receiving and transmitting ultrasound
pulses. As discussed, each reference transducer is separately made
to emit acoustic pulses that are received by each of the other
reference transducers so that the distances d1 through d6 shown in
FIG. 2 are calculated using the respective times it takes for an
acoustic pulse to travel between each pair of the reference
transducers. These distances are triangulated to establish the
positions of the reference transducers relative to each other, and
therefore to establish a three-dimensional coordinate system.
Once a 3-dimensional coordinate system is established in the manner
described, the three-dimensional location of an additional catheter
transducer placed near or within the heart (such as a transducer on
a mapping or ablation catheter 12, 14, or 16) can be calculated as
follows. First, using the "time of flight" method, the distances
between each of the reference transducers T.sub.REF1 through
T.sub.REF4 and the additional catheter transducer (designated
T.sub.CATH in FIG. 2) are established,in parallel. In practice,
these distances are preferably also performed in parallel with the
distance measurements that are made to establish the coordinate
system. Next, using basic algebra and the law of cosines (see,
e.g., the Advanced Mathematics text cited above), the coordinates
of T.sub.CATH relative to the reference transducers are calculated
using the measured distances from T.sub.REF1 through T.sub.REF4 to
T.sub.CATH. This process is referred to as triangulation.
The locations of all or portions of the reference catheters may be
displayed as well. The system is preferably programmed to
extrapolate catheter position from the coordinates of the
transducer locations based on models of the various catheters
pre-programmed into the system, and to display each catheter's
position and orientation on a graphical user display (see display
124 in FIG. 1). The locations of all or portions of the additional
catheters (such as, for example, their distal tips, their
electrodes or ablation sections, if any, or other sections which
may be of interest) are displayed.
The reference catheter(s) 10 thereby establish an internal
coordinate system by which the relative positions of EP catheter
transducers in the heart may be calculated using triangulation and
shown in real-time on a three dimensional display.
Ultrasound Catheters
Catheters of the type which may be used with the system according
to the present invention are shown in FIGS. 3, 9, 13 and 18. These
include a reference catheter 10 (FIG. 2), a marking and ablation
catheter 12 (FIG. 9), a basket-type mapping catheter 14 (FIG. 13),
and a linear lesion ablation catheter 16 (FIG. 18).
Reference Catheters
Referring to FIG. 3, a reference catheter according to the present
invention is an elongate catheter having a plurality of ultrasound
transducers 18 positioned at its distal end. The transducers 18 are
piezoelectric transducers capable of transmitting and receiving
ultrasound signals.
The reference catheters can be integrated with typical EP catheters
by providing the ultrasound transducers described above. This
allows the system to utilize the localization function using
catheters which are already needed for the EP procedure. Thus, use
of the system does not require the physician to use more catheters
than would be used had the EP procedure been carried out without
the localization function.
For example, referring to FIG. 4, the reference catheter 10a may be
an RV apex catheter having a distal pair of EP electrodes 30, an
ultrasound transducer 18a at the distal tip, and additional
ultrasound transducers 18 proximally of the distal tip. It may also
be a coronary sinus reference catheter 10b (FIG. 5) having at least
three bipole pairs of EP electrodes 30 distributed over the section
of the catheter that is positioned in the coronary sinus, and
having at least three ultrasound transducers also distributed over
the section of the catheter that is in the coronary sinus.
Referring to FIG. 6, a preferred transducer 18 is a piezoelectric
cylindrical tube having inner and outer surfaces. The cylindrical
transducer may be made of PZT-5H, PZT-5A, PMN (lead metaniobate or
lead magnesium niobate) or other piezoelectric ceramic
materials.
Electrodes 20 are positioned on the inner and outer surfaces of the
transducer. The electrodes are metal surfaces not limited to
materials such as sputtered chrome and gold, electroless nickel, or
fired silver. The piezoelectric ceramic is polarized in the
thickness mode, i.e., between the two electrodes 20.
The cylinder includes an outside diameter (designated "OD" in FIG.
6) of approximately 0.040 to 0.250 inches, and preferably
approximately 0.060 to 0.090 inches. The cylinder has a length L of
approximately 0.020 to 0.125 inches and preferably approximately
0.030 to 0.060 inches. Wall thickness W is approximately 0.004 to
0.030 inches and preferably approximately 0.006 inches to 0.015
inches. The transducers 18 are spaced from one another along the
catheter 20 (FIG. 3) by a distance of approximately 0.5-10 cm, and
most preferably 1-3 cm.
Preferably, the localization system is operated using the same
operating frequencies for all transducers. The optimal operating
frequency for the system is determined by considering the resonant
frequencies of the ultrasound transducers used for the catheters in
the system. It has been found that, given the dimensions and thus
the resonances of the preferred transducers being used in the
system, the transducers are most preferably operated at a frequency
of approximately 1.0-3.0 MHz, which in the case of the transducer
18 is the transducer resonance in the length mode. Transducer 18
further has a beam width of approximately 114.degree., where the
beam width is defined as the angle over which the signal amplitude
does not drop below 6 dB from the peak amplitude. If desired, a
diverging lens 22 (FIG. 7), in the form of a spherical bead of
epoxy or other material may be formed over the ceramic cylinder to
make the signal strength more uniform over the beam width.
Referring to FIG. 8, the reference catheter transducers 18b may
alternatively be formed of piezoelectric polymer films of
copolymers such as PVDF. Such films would have thicknesses of
approximately 0.005-1.0 mm, and preferably approximately
0.007-0.100 mm, and would preferably include gold film electrodes
on the inner and outer surfaces. As shown in FIG. 8, the polymer
film would be wrapped around a mandrel 24 (which may be part of the
catheter shaft 10c itself or a separate polymer plug inside the
catheter 10). A transducer configuration of this type operates with
a very large band width and does not have a specific resonance due
to the polymer piezoelectric.
Electrode leads (not shown) are attached to the inner and outer
transducer electrodes (such as electrodes 20 of FIG. 6). If
piezoelectric ceramics are used as in FIGS. 6 and 7, leads may be
attached using low temperature solders which typically contain
large proportions of indium metal. Leads may alternatively be
attached with silver epoxy. It is important that the leads be
attached using a minimum amount of material to minimize distortion
of the acoustic field. In the case of the polymer transducers of
FIG. 8, photo lithographic techniques are typically used to create
electrodes and their associated lead tabs. In this manner, the one
side electroded polymer at the tab site does not contribute to the
acoustic field. Leads are typically attached to these tabs with
either low temperature indium based solders or with silver epoxy.
Therefore, for these polymer transducers, the amount of material on
the connection tab does not affect the acoustic field.
The reference catheter preferably includes at least four such
transducers so that a three-dimensional coordinate system can be
established using a single catheter. If desired, the reference
catheter may have more transducers or it may have fewer transducers
if more than one reference catheter is to be used to establish the
three-dimensional coordinate system. Using more than four reference
transducers is advantageous in that it adds redundancy to the
system and thus enhances the accuracy of the system. When more than
four reference transducers are used, the problem of determining the
location of catheter transducers is over determined. The additional
redundancy may provide greater accuracy if the measured distances
between the reference transducers and catheter transducers are
noisy. The overdetermined problem can be solved using
multi-dimensional scaling as described in "Use of Sonomicrometry
and Multidimensional Scaling to Determine 3D Coordinates of
Multiple Cardiac Locations: feasibility and implementation",
Ratciffle et. al, IEEE Transactions Biomedical Engineering, Vol.
42, no. 6, June 1995.
Referring again to FIG. 3, a connector 32 enables the catheter 10
to be electrically coupled to the ultrasound ranging hardware 116
(described below and shown in FIG. 1).
Four twisted pairs 26 of Teflon coated forty-two gauge copper wire
(one pair can be seen in the cutout section shown in FIG. 3) extend
from connector 32 through the catheter 10. Each twisted pair 26 is
electrically coupled to a corresponding one of the ultrasound
transducers 18, with one wire from each pair 26 coupled to one of
the transducer electrodes 20 (FIG. 6). When a transducer is to act
as an ultrasound transmitter, a high voltage pulse (i.e,
approximately 10-200V) is applied across the corresponding twisted
pair 21 and causes the transducer 18 to generate an ultrasound
pulse. When a transducer is to act as an ultrasound receiver, the
ultrasound ranging hardware 116 (FIGS. 27A-27B, described below)
awaits receive pulses of approximately 0.01-100 mV across the
twisted pairs corresponding to receiving transducers. Additional
leads (not shown) couple the EP electrodes 30 to the EP hardware
114 (FIG. 1).
To facilitate manipulation of the reference catheter through a
patient's vessels and into the heart, the reference catheter 10 may
have a pre-shaped (e.g. curved) distal end.
Marking/Ablation Catheter
Referring to FIG. 9, the system of the present invention preferably
utilizes a catheter 12 to identify the locations of anatomical
landmarks (such as the septal wall) relative to the coordinate
system so that the landmarks may be included on the
three-dimensional display. Showing anatomical landmarks on the
display correlates the three-dimensional coordinate system to
discrete anatomical locations and thereby assists the physician in
navigating EP catheters to the desired locations within the
heart.
The marking catheter 12 is preferably a 7 French steerable catheter
having one or more ultrasound transducer(s) 34 mounted at or near
its distal tip. Preferably, the catheter 12 includes one transducer
at or near its distal tip and a second transducer spaced from the
distal tip by approximately 0.5-4.0 cm. The marking catheter 12
need not be one which is limited to use in marking anatomical
sites. It can be a catheter useful for other purposes as well; the
term "marking catheter" is being used in this description as a
matter of convenience. Catheter 12 may also include an ablation
electrode 36 at its distal tip, so that it may also be used to
ablate tissue while the position of the ablation electrode 36 is
tracked using the localization system 100. It may also include
other electrophysiology electrodes 38 which may be used for pacing
and/or mapping as desired by the user.
The transducers 34 may be similar to the reference catheter
transducers 18. While the outer diameter and wall thickness of the
transducers 34 may differ from that of transducer 18 to accommodate
mounting requirements, the length of the transducers 34 is
preferably the same as that of the transducers 18 to assure a
common operating frequency of approximately 1.0-3.0 MHZ.
Alternatively, the more distal transducer might be packaged
differently than the reference catheter transducers. For example,
referring to FIG. 10, the transducer 34 may be mounted just
proximal of the distal ablation tip 36. Alternatively, a
cylindrical transducer 34a or a plate transducer 34b may be
positioned inside the distal ablation tip, in FIGS. 11 and 12,
respectively. An internal piezoelectric transducer would be
embedded in a bead of epoxy 40 positioned in the catheter tip. This
bead would preferably have a spherical contour across the distal
end so that it would act as a divergent lens for the ultrasound
energy. The metal forming the ablation tip 36 must be very thin
(i.e., less than a small fraction of a wavelength) to facilitate
the transmission of acoustic energy to and from an internal
transducer.
The marking catheter 12 may additionally be provided with EP
electrodes 38. As shown in FIG. 9, a handle 42 and a knob 44 for
actuating a pull wire (not shown) allow the marking catheter 12 to
be maneuvered through a patient's vessels and heart using
conventional steering mechanisms. A connector 46 enables the
catheter 12 to be electrically coupled to the EP hardware 114 and
the ultrasound ranging hardware 116 (described below, see FIG.
1).
Mapping Catheter
FIG. 13 shows a first embodiment of a mapping catheter 14 for use
with the system according to the present invention. The catheter 14
is of the type known in the art as a "basket" catheter. It includes
an elongate shaft 48 carrying a mapping basket 50 at its distal
end. The basket 50 is formed of preferably eight arms 52. Arms 52
are constructed of ribbons of a shape memory material such as
Nitinol. The shape memory material is treated such that the ribbons
assume the basket structure shown in FIG. 13 when in an unstressed
condition.
The arms 52 may be concentrated at one section of the basket (FIG.
14A) so that during use mapping may be concentrated in one area of
a cardiac chamber. The arms may alternatively be uniformly spaced
as shown in FIG. 14B. Basket catheters of these types are shown and
described in U.S. Pat. No. 5,156,151, the disclosure of which is
incorporated herein by reference.
A sheath 54 is disposed around shaft 48. Sheath 54 is
longitudinally slidable between the proximal position in FIG. 13
and a distal position in which the basket 50 is compressed within
it. During use the sheath 54 is moved to the distal position to
compress the basket before the catheter 14 is inserted into the
patient, so that the basket can be easily moved through the
patient's vessels and into the patient's heart. Once the basket is
within the desired chamber of the patient's heart, the sheath is
withdrawn, the basket is opened into its expanded condition,
(either by spring action of the arms 52 or by a separate actuator)
and the arms to map electrical activity of the chamber wall.
Each arm 52 of the basket catheter 14 carries a plurality of EP
mapping electrodes 56 designed to detect the electrical activity of
underlying cardiac tissue. A plurality of ultrasound receiving
transducers 58 are also mounted to each arm 52. Preferably, the
mapping electrodes 56 and the ultrasound transducers 58 alternate
with each other along the length of each arm 52, although there
need not be one-to-one correspondence between the transducers and
electrodes.
FIG. 16 is a plan view of one arm 52 of basket catheter 14, and
FIG. 17 is a side section view of the arm of FIG. 16. As shown, the
mapping electrodes 56 and ultrasound transducers 58 are preferably
formed on a flex circuit 60 which is attached to the arm 52. Copper
leads 62 are formed on the flex circuit and each lead is
electrically connected to one of the EP electrodes 56 and one of
the ultrasound transducers 58, and to the EP and localization
hardware 110 (FIG. 1). Each arm 52, including its associated flex
circuit 60, is covered in polyethylene shrink tubing 64, with only
the electrodes 56 being exposed through the shrink tubing 64.
Referring to FIG. 16, a preferred piezoelectric transducer for the
mapping catheter comprises a flat piezoelectric ceramic plate 66.
The plate 66 may be made of PZT-5H, PZT-5A, PMN (lead metaniobate
or lead magnesium niobate) or other piezoelectric materials.
The transducer includes a depth D and length L, each of
approximately 0.010 to 0.060 inches, and preferably approximately
0.025 to 0.040 inches. The transducer has a wall thickness W of
approximately 0.004 to 0.030 inches and preferably approximately
0.006 to 0.015 inches. The length and depth resonances of the
transducer fall in the range from 1.0 MHz to 3 MHz and thus
contribute to the overall performance of the system. The beam width
considerations are the same as those described above for the
reference catheter transducers 18 (FIG. 6).
Electrodes 68a, 68b are positioned on the upper and lower flat
surfaces of the plate. The electrodes are metal surfaces not
limited to materials such as sputtered chrome and gold, electroless
nickel, or fired silver. The piezoelectric ceramic is polarized in
the thickness mode, i.e., between the two electrodes.
The mapping catheter transducers 58 may alternatively be formed of
piezoelectric polymer films of copolymers such as PVDF. Such films
would have thicknesses of approximately 0.005-1.0 mm, and
preferably approximately 0.007-0.100 mm, and would preferably
include gold film electrodes on the inner and outer surfaces. The
polymer film would preferably be taped to the printed wiring board
of the basket arm, and leads attached to the top electrodes in a
manner similar to that mentioned above for the reference catheter
transducers. Alternatively, the polymer film could be used to form
the entire flex circuit.
Lead wires 70a, 70b extend between the copper leads 62 and the
electrodes 68a, 68b. It is important to note that each of the leads
62 electrically connects both an ultrasound transducer 58 and an EP
electrode 56 to the EP and localization hardware 110. Each lead 62
therefore carries electrical activity measured by EP electrodes 56
as well as receive signals from the ultrasound transducers 58 to
the hardware 110. It is possible to do this because EP signals have
a lower frequency (i.e., on the order of 1 Hz-3 kHz) than the
ultrasonic signals, which have frequencies of approximately 500
kHz-30 MHz. Thus, the EP signals can be removed from the recorded
signal using low-pass filtering while the ultrasound signal can be
removed using high pass filtering.
Combining EP and ultrasound signals on the same lead 62 has the
advantage of reducing the total number of conductors in the
catheter 14. While this is advantageous, it is not a requirement
for functionality of the system. Naturally, the system may also be
provided using separate leads for the EP and ultrasound
signals.
For both piezoelectric ceramic and polymer transducers, one lead
70b will most typically be attached by bonding the bottom electrode
68b of the piezoelectric (e.g., plate 66) with silver epoxy to the
printed circuit of the basket arm. Leads 70a may be attached to the
top electrodes 68a in a manner similar to that set forth with
respect to the reference catheter transducers. For the
piezoelectric ceramics 66, the top lead 70a may be attached with
low temperature solders which typically contain large proportions
of indium metal. It is important that the leads be attached using a
minimum amount of material to minimize distortion of the acoustic
field. Top leads 70a may also be attached with silver epoxy. In the
case of the polymer piezoelectrics, metallization of the electrodes
and leads is typically achieved using photo lithographic
techniques. In this manner, the one side electroded polymer at the
lead site does not contribute to the acoustic field as discussed
previously for the polymer transducer of the reference
catheter.
Acoustic wave propagation does not occur across a vacuum or air
gap, consequently it is necessary to provide a rubber path or a
path through an insulating polymer in order to fill air gaps around
the transducers. For example, after the top lead 70a has been
attached, the entire top surface and surrounding areas including
the inner surface of the shrink tubing is coated with a rubber
primer. Subsequently, the area between and around the top surface
of the piezoelectric and the shrink tubing is filled with a
silicone rubber material.
Alternatively, the top surface of the piezoelectric and the
electrical lead may be coated with an insulating polymer. After the
heat shrink tubing is attached to the basket strut, a small area
over and around the top electrode of the ceramic may be cut out of
the shrink tubing to provide an unobstructed exposure of the
transducer to the blood field.
The EP electrodes 56 are preferably platinum black electrodes
having a size of approximately 0.009.times.0.030 inches. For these
small electrodes, platinum black is used for low impedance, i.e.,
approximately less than 5.0 k Ohms over the frequency range
(approximately 1 Hz-3 kHz) of interest for EP signals. This is
important in that it prevents the impedance of the ultrasound
transducers from loading the output of the EP electrodes.
FIG. 15 is a cross-section view of the portion of the catheter 14
which is proximal of the basket 50. The catheter shaft 48 is formed
of an inner shaft 72 and an outer, braided shaft 74 preferably made
from stainless steel braid of a type conventionally known in the
art. The inclusion of the braid improves the torque characteristics
of the shaft 48 and thus makes the shaft 48 easier to maneuver
through patient's vessels and heart.
Inner shaft 72 includes a center lumen 76 through which ribbon
cables 78 extend. Leads (not shown) are formed on the ribbon cables
78 and function to carry signals corresponding to signals received
by the ultrasound transducers 58 and by the electrophysiology
electrodes 56 to the system hardware 110 (FIG. 1). An ablation
catheter lumen 80 extends through the shaft 48 and allows an
ablation catheter such as catheter 12 to be introduced through the
shaft 48 and into contact with tissue surrounding the basket
50.
Inner shaft 72 further includes a deflection lumen 82. A pull wire
(not shown) extends through the deflection lumen 82 and facilitates
steering of the basket using means that are conventional in the
art.
Linear Lesion Ablation Catheter
FIGS. 18 through 26 show a linear lesion ablation catheter 16 for
use with the system 100 of the present invention. Catheter 16 is an
elongate shaft preferably constructed of a thermoplastic polymer,
polyamid ether, polyurethane or other material having similar
properties. An ablation section 84, the section of the catheter 16
at which ablation is carried out, is located at the distal end of
the shaft.
As shown in FIG. 18, an elongate window 86 is formed in the wall of
the ablation section 84. The window 86 may be made from heat shrink
polyethylene, silicone, or other polymeric material having a
plurality of small holes or perforations formed in it. It may
alternatively be formed of the same material as the remainder of
the shaft and simply include a plurality of holes formed through
it.
Referring to FIG. 19, a foam block 88 is disposed within the
catheter, next to the window 86. The foam block 88 is formed of
open cell polyurethane, cotton-like material, open-cell sponge,
hydrogels, or other foam-like materials or materials that are
permeable by conductive fluids. A plurality of RF ablation
electrodes 90 line the edge of the foam block 88 such that the foam
block lies between the electrodes 90 and the window 86.
Ultrasound transducers 92 are positioned at the distal and proximal
ends of the foam block 88. The transducers 92 are preferably formed
of piezoelectric ceramic rings having electrodes bonded to their
inner and outer surfaces, although the transducers may also be
formed in a variety of alternative shapes.
Referring to FIGS. 20-22, several lumen extend through the catheter
16. The first is a fluid lumen 94 that extends the length of the
catheter 16 and is fluidly coupled to a fluid port 96 (FIG. 18) at
the proximal end of the catheter. It should be noted, with
reference to FIG. 20, that the walls of the fluid lumen are cut
away at the ablation section 84 to accommodate placement of the
foam block 88 and the RF electrodes 90 within the catheter.
A pair of lead lumen 98 house lead wires 100 that carry RF energy
to the electrodes 90 and lead wires 102 that carry voltage signals
from the transducers 92. A fourth lumen 104 houses a Nitinol core
wire 106 which provides rigidity to the catheter.
Because breaks in a linear lesion can reduce the success of an
ablation procedure by leaving a path through which current may
travel during atrial fibrillation episodes, the fluid lumen, foam,
and window are provided to improve the coupling of the RF energy to
the cardiac tissue to minimize the likelihood of breaks in the
lesion.
Specifically, during use, the window 86 of ablation section 84 of
the apparatus is positioned adjacent to the body tissue that is to
be ablated. RF energy is delivered to the electrodes 90 while
saline or other conductive fluid is simultaneously delivered
through the fluid lumen 94. The conductive fluid passes out of the
fluid lumen 94 and into the foam 88, and contacts the electrodes
90. The fluid also flows through the window 86 into contact with
the body tissue, thereby improving the coupling of the RF energy
from the electrodes 90 to the tissue and improving the efficiency
of the ablation of the tissue.
Using a conductive liquid dispersed over the desired area as a
mechanism for coupling RF energy to the tissue produces lesions
having greater continuity (and thus fewer breaks through which
current can pass during atrial fibrillation episodes) than lesions
formed by apparatuses that rely solely on direct contact between
the electrodes and the body tissues, decreasing the likelihood of
thrombus formation on the electrodes and thus decreasing the chance
of an embolism. The foam and the window improve ablation in that
the conductive liquid is uniformly dispersed within the foam and
then is focused onto the body tissue as it passes through the holes
or pores in the window. This concept, and several alternate ways of
configuring linear lesion catheters that may be adapted to include
ultrasound transducers and used in the system of the present
invention, are described in published International Application
PCT/US96/17536, the disclosure of which is incorporated herein by
reference.
FIGS. 23 and 24 show a first alternative embodiment of a linear
lesion catheter according to the present invention. The first
alternative embodiment 16a differs from the embodiment of FIG. 19
primarily in the shape and placement of the transducers.
Transducers 92a of the first alternative embodiment are
piezoelectric chips embedded within the foam block 88. Each
transducer 92a includes a pair of electrodes on its opposite faces
and is encapsulated in an insulating cocoon 108 of epoxy, acrylic,
or silicone rubber which prevents the fluid in the foam from
creating a short circuit between the electrodes.
A second alternative embodiment of a linear lesion catheter
according to the present invention is shown in FIGS. 25 and 26. The
second alternative embodiment also differs from the preferred
embodiment only in the form and placement of the transducers. Each
transducer 92b and its leads 102b is inside an epoxy capsule 109
embedded in the foam block 88. It should be noted, then, that only
the RF electrode leads 100 extend through the lumen 98. The leads
102b of the second alternative embodiment extend through fluid
lumen 94 as shown.
System Components
Referring to FIG. 1, the system 100 generally includes
amplification and localization hardware 110, catheters 10, 12, 14
and 16, and a microprocessor workstation 112.
Hardware 110 includes conventional signal amplifiers 114 of the
type used for electrophysiology procedures (for example, the Model
8100/8300 Arrhythmia Mapping System available from Cardiac Pathways
Corporation, Sunnyvale, Calif.). It also includes ultrasound
ranging hardware 116 and an ultrasound hardware control and timing
component 118 which together initiate, detect, and measure the time
of flight of ultrasound pulses emitted and received from the
ultrasound transducers on the reference and EP catheters 10-16.
Signal amplifiers 114 and the ranging hardware 116 and controller
118 are electronically coupled to a microprocessor workstation 112.
The microprocessor work station 112 is designed to control the
system hardware and the data processing for both the EP and
ultrasound functions of the system, and to generate a visual
display of EP and catheter position data for use by the
clinician.
For EP functions, the microprocessor 112 includes an amplifier
controller 120 that delivers mapping, and/or pacing commands to the
EP signal amplifiers 114. Signal processors 122 receive data
corresponding to electrical activity measured by the mapping
catheters 14, 16 and generate graphical representations of the
measured data for display on graphical interface display 124. The
mapping signals shown on the graphical display can represent any
number of parameters or characteristics, such as measured signal
values or impedance values, indicators of electrode contact, or
indicators of the probability that there is an arrhythmogenic site
in the area, etc.
Ultrasound hardware controller 118 and a triangulation processor
126 control the catheter localization functions and data
processing. During use, controller 118 directs the ultrasound
ranging hardware 116 to initiate an ultrasound pulse from a
selected transmitting transducer. It further directs the hardware
116 to (1) detect, in parallel, voltages corresponding to reception
of the ultrasound pulse by the receiving transducers, and (2)
measure the elapsed time (time of flight) between transmission of
the ultrasound pulse and its detection by the selected receiving
transducers. Triangulation processor 126 receives data
corresponding to these time of flight measurements from the ranging
hardware 116 and uses it to calculate the locations of the EP
catheter transducers relative to the reference transducers (see
Localization System Overview). Data corresponding to catheter
position, as calculated from transducer locations, and measured EP
signals is shown in graphical form on graphical user interface
display 124.
The ultrasound ranging hardware 116 may be configured to detect an
acoustic pulse received by a receiving transducer in a number of
ways. For example, if the transmitting transducer is made to
generate a short burst of high frequency ultrasound energy, the
hardware 116 may be configured to detect the first signal excursion
above or below a predetermined maximum and minimum voltage
threshold, or the peak of a received signal. Alternatively, the
transducer may be made to generate a continuous wave of low
frequency ultrasound, in which case the hardware 116 would be
configured to measure the difference in phase between the standing
wave as generated by the transmitting transducer and as detected by
the receiving transducer.
Referring to FIG. 27A, the ultrasound ranging hardware 116 includes
a plurality of channels 128a, 128b, each of which is electronically
coupled to one of the ultrasound transducers in the system.
Depending on whether a transducer is intended to transmit and
receive ultrasound signals (as in the case of a reference catheter
transducer 18) or to receive ultrasound signals only (as in the
case of an additional catheter transducer 34, 58 or 92), a
transducer's corresponding channel circuitry may be configured to
permit transmission and receipt of ultrasound signals by the
transducer, or it may be configured only to allow receipt of
signals by the transducer. Accordingly, transmit/receive channels
128a are each connected to a corresponding one of the reference
catheter transducers 18 (FIG. 3), and receive channels 128b are
each connected to a catheter transducer 34, 58, 92 (e.g., FIGS. 9,
13 and 19).
Referring to FIG. 27B, the circuitry of each of the channels 128a,
128b generates digital data corresponding to the time of flight of
an ultrasound transmit pulse from a transmitting transducer to the
transducers corresponding to each of the channels 128a, 128b. Each
channel 128a, 128b includes an amplifier 130 which amplifies
voltage signals generated by the ultrasound transducers in response
to receive pulses. The transmit/receive channels 128a additionally
include transmitters 132 which, in response to signals from
transmit and receive controller 142 (discussed below), apply
voltages across the reference transducers 18 to trigger ultrasound
pulses.
Each channel 128a, 128b further includes a threshold detector 134
which triggers a latch 136 once a received signal exceeds a
threshold level. Latch 136 is coupled to distance register 138
which is in turn coupled to place distance output data onto data
bus 140 upon activation of the latch 136.
Ultrasound hardware control and timing component 118 includes
transmit and receive controller 142. Controller 142 is
electronically coupled to a system clock 141 that drives a distance
counter 144, and to a threshold amplitude generator 146 which
provides the threshold reference input for threshold detectors
134.
As will be discussed in greater detail, count values from the
distance counter 144 are used by the system of the invention to
calculate the distances between transmitting transducers and
receiving transducers. Because system clock 141 drives the distance
counter 144, it is the frequency of the system clock that
determines the resolution of measured distances between
transducers. The higher the frequency of the clock, the greater the
resolution of the distance measured. Clock 141 is therefore a high
frequency counter which preferably operates at least approximately
5-50 MHz, which is equivalent to a resolution of approximately
0.3-0.03 mm.
The threshold amplitude generator 146 produces time varying
positive and negative thresholds that are used as inputs to the
threshold detectors 134 of each channel 128a, 128b. Preferably, one
threshold amplitude generator 146 is used for the entire system in
order to minimize the amount of hardware in the system. However,
the system may alternatively use a separate threshold amplitude
generator for each channel, or separate threshold amplitude
generators for different groups of channels. For example, different
threshold amplitude generators may be used for different types of
receiving transducers, since some produce weaker signals and
therefore require lower thresholds. As another alternative, a fixed
threshold may be used together with a variable gain amplifier in
place of amplifier 130.
The threshold amplitudes are preferably varied by the threshold
amplitude generator 146 so that they are large at the time a
transmit pulse is initiated and so that they decrease as time
passes following transmission of a pulse. Using a variable
threshold rather than a fixed one is beneficial because the dynamic
range (i.e., the ratio of the largest signal to be detected to the
smallest signal to be detected) is quite large, and may even be as
high as 70 dB due to factors such as anisotropy of the transit and
receive beam profiles, signal decay due to ultrasound wave
propagation, and attenuation of the signal caused by blood and
tissue. Because transducer receiving wires for a catheter based
system must be closely spaced, a fixed dynamic range of this
magnitude could lead to erroneous data, because cross-talk between
the closely spaced receiving wires could be interpreted by the
system to be actual receive signals.
It should be noted that both positive and negative thresholds are
used so as to increase the accuracy of the detection time, since a
negative oscillation of a transmit pulse may reach the detection
threshold before a positive oscillation. Latch 136 will therefore
be triggered by whichever of the positive or negative thresholds is
achieved first.
When a transmit pulse T (FIG. 28A) is being sent to a transducer,
oscillation, or "ringing", designated "R.sub.T ", can occur on the
corresponding twisted pair 26 (FIG. 3). The ringing in the transmit
line is not problematic in and of itself. However, in catheters
such as the reference catheter 10 which includes transducers which
can both transmit and receive ultrasound signals, the close
proximity of the transmitting and receiving lines can cause the
ringing to cross over to the receiving line. This problem arises
most frequently when the system is computing the relative
orientations of the reference transducers 18 (FIG. 3) in order to
establish the three-dimensional coordinate system, since that
procedure requires measuring the time it takes for a pulse emitted
by one of the reference transducers 18 to be received by the other
reference transducers 18 on the same catheter. The ringing (which
is designated "R.sub.R " in FIGS. 28B and 28C) can be of similar
magnitude to a receive signal "S" and can therefore make it
difficult to determine whether a receive signal has been
detected.
If the transmitting and receiving transducers are far apart, a
receive signal on a receiving line (such as twisted pair 26) will
be measured by the ultrasound system circuitry despite the ringing,
because transmission of the receive signal on the receiving line
will happen only after the ringing has diminished. See FIG. 28B.
However, if the transmitting and receiving transducers are close
together (i.e., separated by less than approximately 2 cm), the
receive pulse will be lost in the ringing on the receive line,
because the receive pulse will reach the receiving line while the
ringing is still occurring. See FIG. 28C.
It has been found that this problem may be avoided by including
circuitry which will short the conductors of the transmit line
immediately after the transmit pulse is sent. An example of such
circuitry is shown in FIG. 29. The circuit includes the pulse
generator 148 and center tapped transformer 150 which comprise
basic pulse generating circuitry, plus a switch 152 which is closed
immediately after a transmit pulse in order to short the ringing to
ground. A small impedance 154 is placed in series with the switch
in order to dampen the ringing through the short circuit. As
illustrated in FIGS. 28D and 28E, by eliminating the ringing from
the transmitting line, the switch eliminates the ringing from the
receiving line as well.
Referring again to FIG. 27B, during use of the system, each
transmit/receive channel 128a is sequentially selected for
transmission of a transmit pulse, and all channels 128a, 128b are
simultaneously selected for parallel reception of distance data.
Transmit and receive controller 142 selects which of the
transmit/receive channel 128a will initiate an ultrasound pulse,
and cycles through each transmit/receive channel, causing
sequential transmission of pulses by the reference transducers 18
(FIG. 3). It uses the system clock 141 to generate a lower
frequency transmit clock, which in turn controls how often
ultrasound pulses are transmitted.
Each time a transmit pulse is to be initiated, the transmit and
receive controller 142 performs the following sequence of steps.
The distance counter 144 is first reset to zero, and the threshold
amplitude generator 146 is reset. A detection hold off and reset
signal is next sent by controller 142 to all channels 128a, 128b.
This resets the latch 136 for each channel and prevents it from
latching for a specified time period to prevent detection due to
electromagnetic coupling of ringing after transmission of a
transmit pulse. This "hold off" period is determined by the
smallest distance within the patient that is to be measured, and is
calculated according to the following equation:
Thus, if the smallest distance to be measured is 10 mm, the "hold
off period" is: ##EQU1##
After the hold off and reset signals, a transmit control signal is
sent to a selected one of the transmit/receive channels 128a,
causing it to initiate a transmit pulse. Shortly afterwards, a
signal is sent to the same transmitter to initiate damping in order
to prevent/reduce ringing as described above.
When a transmit pulse is initiated, the distance counter 144 is
simultaneously activated. After a transmit pulse is triggered, each
channel 128a, 128b "listens for" a receive pulse. When the
threshold detector 134 for a particular channel detects a receive
pulse that exceeds the threshold set by the threshold amplitude
generator 146, the latch 136 for that channel is activated. Once
the latch 136 is activated, a load data command is sent to the
associated distance register 138 and the current contents of the
distance counter 144 are loaded into the distance register 138 for
that channel. This data is subsequently placed on the distance data
bus 140 along with data indicating which channel transmitted the
pulse. Thus, the data bus receives a number of distance values
which correspond to the number of transmit/receive and receive only
channels. These distance values are then used by the triangulation
processor 126 (FIG. 1) to determine the relative positions of the
ultrasound transducers, and the microprocessor 112 uses the
position data to create a three-dimensional display of the
catheters.
Graphical Display Features
As described, the three-dimensional positions of the integrated
ultrasound transducers (such as those on catheters 10, 12, 14 and
16) may be continuously displayed in real-time on the graphical
user interface display 124 (FIG. 1). The three-dimensional
positions of the catheters (10, 12, 14 and 16), or portions
thereof, may also or alternatively be continuously displayed based
on the position of the transducers by extrapolating the catheter
position using a known model of the catheter programmed into the
system. The three-dimensional positions of the transducers and/or
catheters may also be stored in the system's memory and selectively
displayed on the graphical display user interface display 124 as
required during a procedure.
For example, data corresponding to electrode locations on a mapping
basket 14 may be saved in the system memory, together with data
representing EP measurements taken by EP electrodes corresponding
to the transducer locations. If, after the mapping basket 14 has
been removed from the patient, the user wishes to guide an ablation
catheter to a location corresponding to one of the basket
electrodes, s/he may elect to display the saved location
information for the basket simultaneously with the real time
position of the ablation catheter.
The graphical user interface is further provided with several
additional functions that improve the accuracy and usefulness of
the system.
For example, the microprocessor 112 includes software which
enhances the accuracy of the system by "gating out" the effects of
cardiac motion on the position data calculated for the transducers
and/or catheters. Because a beating heart contracts and expands
with each beat, the catheter will move with the heart throughout
the cardiac cycle even when a catheter is at a mechanically stable
location within the heart. Thus, a real time display of the
catheter (or transducer) position would show the catheter or
transducer moving on the display because of the cardiac
movement.
Such movement of the catheter/transducer on the display does not
present problems in and of itself. However, if the user elects to
save in the system memory the position of the catheter so that it
may be used later during the procedure (such as to indicate
anatomical landmarks, ablation locations, mapping locations, etc.),
the effects of the movement on the saved locations can lead to
inaccuracies if the user attempts to navigate a catheter (shown in
real time on the display) with respect to the representation on the
graphical display of the previous catheter position data.
To eliminate this problem, the patient's electrocardiogram (EKG) is
monitored during use of the system, and the EKG is used to
synchronize the acquisition of position data so that all position
data is acquired at the same point in the cardiac cycle. Thus, for
example, when EP signals are recorded from catheters having
integrated localization transducers, the relative position/location
information for the EP electrodes is accurate when displayed
because all of the location information will have been collected
during the same phase of the cardiac cycle. Gating is similarly
carried out for the ablation and marking catheters, by collecting
the appropriate position/location data for such catheters and the
anatomical landmarks during the same phase of the cardiac
cycle.
FIG. 30B shows an EKG signal along with corresponding electrode
position data recorded over the cardiac cycle. It has been found
that the end of diastole, at the Q-R wave of the EKG signal, is a
convenient point for gating the position measurements. FIG. 30A
schematically shows a gating system in which a patient's EKG signal
is passed through an amplifier 302 and a detector 304 which
initiates a sample and hold sequence 306 of position data when the
initiation of a Q-R wave is detected.
The user preferably has the option of showing the gated position,
or the actual (moving) position, or both on the real time display.
The actual position of a catheter may be useful for assessing
whether a catheter is in firm contact with the wall of the heart,
because if the catheter is spaced away from the wall it will not
move with the wall. A display of actual position may also be
helpful during steering of a catheter because it provides more
rapid feedback of a catheter's position and orientation.
It should be emphasized, however, that gated position information
is essential during navigation of a catheter to a location which
has been saved in the three-dimensional display, because unless the
catheter position and the stored location are gated to the same
point in the cardiac cycle, the user cannot be certain that the
catheter has been navigated to the proper location.
Similarly, if EP signals are to be displayed in the form of an
isochronal map on the three-dimensional display, the position used
in the isochronal map to display an activation time for that
location should be an EKG gated location.
Similar gating may also be provided to eliminate inaccuracies in
location information due to the rising and falling of the chest
during respiration. For respiratory gating, chest movement would be
monitored using a bellows or other device and the sample and hold
sequence would be triggered at a desired portion of the respiratory
cycle.
Referring to FIG. 31, the gated positions of lesions and anatomical
landmarks may be stored in the system software and added and
deleted from the display as needed by the user by manipulating a
cursor using a mouse or other user input device to the appropriate
item in marker box 156.
The microprocessor 112 is preferably further provided with software
which allows the physician to manipulate the display in many ways
so that the maximum benefit may be obtained from the system. For
example, referring again to FIG. 31, the user can rotate the
display in three-dimensions by guiding the cursor to the
appropriate icon in manipulation box 158. The user may likewise
"zoom" towards or away from the image in the same manner. S/he may
also elect which of the catheters 10, 10a, 12, 16 to display in
real time using real time box 156.
The system further allows the user to select one of the standard
orientations used in fluoroscopy such as anterior-posterior ("AP"),
lateral, right anterior oblique ("RAO") or left anterior oblique
("LAO") by selecting the appropriate icon in orientation box 160.
In the RAO view, the plane formed by the aortic-valve ring ("AV
ring") is approximately perpendicular to the plane of the display,
with the end of the coronary sinus pointing to approximately the
2-3 o'clock position on the AV ring. In the LAO view, the apex of
the heart is oriented such that it "points" towards a user viewing
the display.
When the system of the invention is used is a preferred mode, the
transducers of a reference catheter positioned in the coronary
sinus ("CS reference catheter") define the AV ring, and the distal
tip of a second reference catheter is positioned in the RV apex
("RV apex catheter"). The system can orient the display to an RAO
orientation by deriving the location of the AV ring from the
location of the transducers on the CS reference catheter, and
re-orienting the display until the AV ring is perpendicular to the
display and until the distal tip of the CS reference catheter
points towards the 2 o'clock position.
With the AV ring perpendicular to the display, the system may also
display straight anterior, posterior, left lateral, and right
lateral views by orienting the CS catheter distal tip at the 12
o'clock, 6 o'clock, 3 o'clock, and 9 o'clock positions,
respectively.
Similarly, the system can orient the display to an LAO orientation
by deriving the location of the RV apex from the locations of the
transducers on the RV apex catheter, and by orienting the display
so that the RV apex points out of the display.
Operation
Two examples of procedures which may be carried out using the
system of the present invention will next be described. It should
be appreciated, however, that the system 100 may be utilized in any
procedure in which three-dimensional navigation of devices relative
to one another is required.
FIG. 33 is a flow diagram giving a sample methodology for using the
system according to the present invention for diagnosis and
treatment of ventricular tachycardia. The steps shown in the flow
diagram will be discussed with reference to the illustrations of
the heart shown in FIGS. 34A through 34D.
First, step 200, a reference catheter is introduced into the
inferior vena cava and is passed under fluoroscopy into the right
ventricle (designated RV). The catheter is positioned with its
distal tip at the apex (A). A second reference catheter 10a is
introduced via the superior vena cava into the coronary sinus (a
vein, shown and designated CS in FIG. 34B, that extends around the
edge of the AV ring separating the left atrium and the left
ventricle). The reference catheters may be positioned elsewhere
without departing from the scope of the present invention. However,
the RV and CS are suitable locations because they allow the
catheters to remain mechanically stable within the heart. Moreover,
these reference catheters will include the EP electrodes equivalent
to those already used on CS and RV apex catheters, i.e. they will
replace conventional CS and RV apex catheters. Placement of the
reference catheters using these approaches therefore does not
require introduction of additional introducer sheaths or catheters
into the patient.
Throughout the procedure, the system calculates the relative
positions of the ultrasound reference transducers 18 (FIG. 3) using
time-of-flight measurements and triangulation, establishes the
three-dimensional coordinate system, and displays at least a
portion of the reference catheter on the graphical interface
124.
Next, referring again to FIG. 34A, marking catheter 12 is
preferably (but optionally) introduced into the left ventricle.
Catheter 12 is guided under fluoroscopy to sequentially position
its distal tip against various anatomical landmarks, such as the
apex, septal wall, lateral wall, etc. The location of each
transducer 34 (FIG. 9) relative to the reference catheters is
calculated again using time-of-flight measurements and
triangulation. The location of the catheter distal tip and thus the
location of the anatomical site is extrapolated from the transducer
location using a model of the catheter 12 pre-programmed into the
system, and it may be subsequently displayed on the graphical
display. Once the desired landmarks are identified and displayed,
the marking catheter 12 is removed from the heart. Steps
202-208.
Referring to FIG. 34C, basket catheter 14 (FIG. 13) is next
introduced under fluoroscopy into the left ventricle (LV), at a
location at which the clinician suspects there may be
arrhythmogenic tissue. Step 210. Because the basket arms 52 include
ultrasound transducers 58 as well as mapping electrodes 56, the
locations of the mapping electrodes can be determined relative to
the reference catheters and displayed on the graphical display
based on a model of the basket 50 programmed into the system. Step
212.
Electrical activity within the heart is recorded from the mapping
electrodes 56 and mapping data derived from the recorded activity
is displayed on the graphical display. The EP signal display may be
displayed separately from the three-dimensional display, such as in
the signal display window 162 shown in FIG. 32. Each graph in the
signal display window 162 represents the voltage data over time, as
measured by one of the EP electrodes 56 on the basket catheter
14.
The EP signals may alternatively be displayed in the form of an
isochronal map on the three-dimensional display. A display of this
type would be generated by first placing an activation time on each
signal, where an activation time is the time at which the tissue
under a mapping electrode 56 activates. The activation times can be
either placed automatically using an algorithm or manually by the
user. The map is generated by showing a color on the
three-dimensional display that represents an activation time at a
location corresponding to the location of the electrodes that
measured the signal. It may be in the form of discrete color dots
or an interpolated color surface or sheet which passes through the
locations of the EP electrodes.
The EP display may alternatively take the form of an isopotential
display on the three-dimensional display. An isopotential map is
similar to an isochronal map except that it is a time varying color
display that is proportional to signal amplitude rather than a
static display of activation time.
Other mapping data derived from the EP signals may also be shown on
the display. For example, data indicating the adequacy of contact
between the electrodes and the tissue, or indicating the
probability that there is an arrhythmogenic site at the mapped
location may be represented on the display. The physician may
induce electrical activity for subsequent measurement by pacing the
heart from the basket electrodes 56. Step 214.
If an arrhythmogenic region is identified by the clinician on the
visual display, a marking and ablation catheter 12 (FIG. 9) is
inserted into the center lumen 80 of mapping catheter 14 (FIG. 15)
and is guided into the left ventricle. The three-dimensional
position of the ablation electrode 36 is displayed (using
ultrasound receiving transducer 18 to track its position) in real
time to aid the physician in guiding the electrode 36 to the
arrhythmogenic region of the endocardium. FIG. 34D and step 216.
Once the ablation electrode is positioned at the arrhythmogenic
region, ablation is carried out by supplying RF energy to the
electrode 36.
The clinician next attempts to induce ventricular tachycardia by
pacing the site from the basket catheter electrodes 56 or from
electrodes on another catheter. Step 220. If VT cannot be induced,
the procedure is considered successful and the catheters 10, 14 are
removed. Step 222. If VT is induced, additional mapping and
ablation steps are formed until the VT appears to be
eradicated.
It should be noted that if mapping is carried out using a basket
catheter that is not provided with a center lumen 39, the basket
catheter may be removed after its electrode positions and
corresponding mapping signals (which may include a visual
identification of the arrhythmogenic region) are saved in the
system memory, and a separate ablation catheter may be introduced
into the heart and guided to the arrhythmogenic region identified
on a visual display of the gated positions of the mapping
electrodes.
FIG. 35 is a flow diagram illustrating use of the system according
to the present invention with a linear lesion catheter of the type
shown in FIGS. 18-26 to treat atrial fibrillation. The steps shown
in the flow diagram will be discussed with reference to the
illustrations of the heart shown in FIGS. 36A-36C and the examples
of the graphical user interface shown in FIGS. 31 and 32.
First, reference catheters 10, 10a are placed in the coronary sinus
and RV apex as illustrated in FIGS. 34A and 34B. The reference
catheters 10, 10a are preferably represented on the graphical
display as shown in FIG. 31. Step 300. Although only the reference
transducer positions are precisely known, the catheter locations
can be estimated using the transducer positions, the known spacing
of the transducers along the catheter bodies, and a known model of
the catheter.
Next, referring to FIG. 36A, marking catheter 12 (FIG. 9) is
positioned in the left atrium, preferably by inserting it through a
transeptal sheath passed from the right atrium, through the septum
and into the left atrium. Steps 302-304. Marking catheter 12 is
sequentially positioned with its distal tip at anatomical
landmarks, such as the pulmonary veins, septal wall, mitral valve,
etc.
The location of each ultrasound transducer 34 on the marking
catheter 12 relative to the 3-D coordinate system is calculated
using time-of-flight measurements and triangulation. The position
of the distal tip is extrapolated from the transducer using a model
of the catheter pre-programmed into the system, and is subsequently
displayed on the graphical display when the distal tip is
positioned at a desired anatomical site (as verified using
fluoroscopy), the user adds an appropriate indicator to the display
at the distal tip location by entering the necessary input at
marker box 156 (FIG. 31). For example, see FIG. 31 in which the
left superior pulmonary vein and left inferior pulmonary vein are
identified as "LS" and "LI". After the appropriate landmarks are
added to the 3-D display, the marking catheter 12 is removed from
the heart.
Next, using a mouse or other user input device, lines representing
target locations for linear lesions are added to the display. Step
312. These lines are identified by the dashed lines on FIG. 31. The
linear lesion catheter 16 (FIG. 8) is next inserted into the left
atrium, preferably via the transeptal sheath 87 shown in FIG. 36A.
During placement of the linear lesion catheter, the position of
ablation window 86 (FIG. 19) is tracked in real time by tracking
the positions of the transducers 92 using the localization system
100 and by deriving the window location from the transducer
location. An arrow A1 or other icon representing the length of the
catheter 16 lying between the transducers 92 is shown on the
display as shown in FIG. 31.
Referring to FIG. 36B, lesion catheter 16b (shown in FIG. 36B to
have an ablation section slidable on a looped baffle wire as
described in PCT/US96/17536), is guided using the localization
system 100 to a first one of the desired ablation locations marked
onto the display by the physician. By manipulating the catheter 16
such that the display shows arrow A1 lying over the area marked as
a target location, the physician can ensure that the window 86
through which ablation will occur is at the correct location. If a
different type of ablation catheter is used, including one which
does not involve the use of an electrolytic fluid, the physician
may use a similar procedure to align the ablation section (which
may be an electrode, an electrode array, or another region of the
ablation catheter at which ablation will be carried out) with the
target location.
RF energy is supplied to the RF electrodes 90 (FIG. 19) while a
conductive fluid is supplied to the fluid port 96 (FIG. 18), to
create a linear lesion in the target tissue. Step 318. Arrows A2 or
other icons representing the window 86 positions during each
ablation are added to the display to indicate the location of a
linear lesion. These arrows may be coded by color or other means to
indicate characteristics of the lesion, such as the wattage used to
create the lesion or the impedance during the ablation. The linear
lesion catheter is then repositioned for additional ablation steps
until all of the desired ablation locations have been treated.
Next, the linear lesion catheter is removed, and mapping basket 50
is inserted into the left atrium as shown in FIG. 36C. Steps 322,
324. The positions of basket electrodes and arms are determined
using the ultrasound localization system and are displayed on the
3-D display in the manner described above. FIG. 32 illustrates the
positions of the arms 52 with solid lines and the position of the
recording electrodes 56 with stars. Pacing and mapping is carried
out using the electrodes 56 in a conventional manner to determine
whether the linear lesions have blocked transmission of the
electrical currents that traverse the left atrium during an atrial
fibrillation episode. The electrical activity measured by the
mapping electrodes 56 is shown in the form of an isochronal map
over the lesion locations A2 on the three-dimensional display.
Steps 328-330. If the linear lesions are found to be successful,
the basket catheter is removed and the procedure ended. If
additional lesions are necessary, the locating, the ablating,
pacing and mapping steps are repeated.
One embodiment of the system of the present invention has been
described, and it has been described primarily with respect to EP
catheters and cardiovascular procedures. It should be appreciated,
however, that the system and its components may be used in a
variety of medical and non-medical contexts in which
three-dimensional representation of structures and surfaces is
needed. Thus, the present invention is not to be limited by the
specific embodiments and procedures described herein, but should be
defined only in terms of the following claims.
* * * * *